#define _CRT_SECURE_NO_WARNINGS 1
#include<bits/stdc++.h>
using namespace std;
int sum, money, month;
bool check(double x)
{
	double s = sum;
	for (int i = 0; i < month; i++)
	{
		s = s * (1 + x) - money;
	}
	if (s > 0) return true;
	else return false;
}

int main()
{
	cin >> sum >> money >> month;
	double l = 0, r = 10;
	while (r - l > 1e-4)
	{
		double mid = (l + r) / 2;
		if (check(mid)) r = mid;
		else l = mid;
	}
	printf("%.1lf\n", l * 100);
	return 0;
}